Typical ZAFCs include an alkaline electrolyte, a replaceable supply of zinc at the anode, an air cathode, which typically includes a non-precious metal catalyst, and a polymer separator. ZAFCs require refuelling with fresh alkaline electrolyte and zinc supply, and removal of reaction products such as zinc oxide and zincates.
In general, the current air cathodes available for metal-air and direct alcohol fuel cells do not meet the requirements of catalytic activity, durability and cost that would provide widespread commercialization of these devices.
The prior art includes various catalyst compositions including CoTMPP+MnO2/C, CoTMPP+Co3O4+MnO2/C (U.S. Pat. No. 7,097,933 (2003)), Ag—WC/C (Meng, P. K. Shen. Electrochem. Communications. 8 (2006) 588-594), AgMnO4+5-10% MnO2 (E. Curelop et al., U.S. Pat. No. 6,632,557 (1999)). Also, the combination of WC, Co and Ag with CoTMPP was developed to form complex compositions of bifunctional electrodes for rechargeable zinc air fuel cells, such as (CuSO4+NiWO4+WC+Co)/C (U.S. Pat. No. 3,977,901 (1976), U.S. Pat. No. 4,152,489 (1979)), 46% (3% Ag+7% FeWO4+7% WC+12% Co+7% NiS)/C (U.S. Pat. No. 5,318,862 (1994)), (AgCoWO4+WC+WS2+NiS+10-15% Co)/C+20% PTFE (U.S. Pat. No. 4,431,848 (1982)), [(0.3-2%) CoTMMP/C+(1-4%) Ag+(1-7%) NiS (or WS2)+(4-10%) LaNi1-xCox+(18-32%) CoxOy]+[(1-20%) WC+(1-20%) Co+(1-7%) FeWO4 (or CoWO4)/C (AB-50)] (U.S. Pat. No. 5,306,579 (1994)).
It is noted that the latter reference includes a complex combination of numerous catalytically active materials, including CoTMPP, Ag, WC and other additives, but in a bifunctional electrode for a secondary rechargeable ZAFC cell.
Additionally, US published patent application no. 20040086774 (Munoz et al) discloses fuel cell catalyst compositions including combinations of CoTMPP, Ag and MnO2. However, this is no more than a non-enabled wish list of such compositions. Also, a higher performance cathode (CoTMPP/C with current density j=500 mA/cm2 at 1 V discharge in KOH) is disclosed in W. Yao et al., U.S. Pat. No. 6,368,751 (2002). However, this patent did not show the stability of this active electrode, the concentration of electrolyte in the cell and the pyrolysis temperature of CoTMPP. It showed only general heat treatment at 350° C. for the melting of the Teflon® bonding agent. It is known that non-heat treated catalysts have higher surface area and performance but low durability.
The main limitations of the state-of-the-art air cathodes for ZAFCs are as follows:                Low performance of ZAFC in 30% KOH (single cell voltage <1V at current density of 280 mA/cm2)        Insufficient durability        Insufficient corrosion and liquid penetration resistance        Insufficient bonding between support (specifically metal foam) and composite materials for a more robust electrode structure        